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4. Physics and Natural Laws

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9. Kinetic Energy (cont.)

KE = 1/2 MVKinetic Energy = one-half the Mass times Speed squared

The kinetic energy of your body while it is in motion, of loose objects in the car, and of the car itself, all increase with weight (mass) and the square of your speed so that:

  • if you increase your speed from 10 MPH to 20 MPH, you are dealing with four times the amount of kinetic energy
  • if you increase you speed from 10 MPH to 50 MPH you have to deal with 25 times the amount of kinetic energy

  • Kinetic Energy's effect on stopping distance

    The kinetic energy of your moving vehicle determines your ability to stop the car. In addition to the distance traveled due to your reaction time, your stopping distance will be:

  • four times further if you increase your speed from 10 MPH to 20 MPH
  • 25 times further if you increase your speed from 10 MPH to 50 MPH.

  • Applying the brakes causes friction. Friction produces heat . The friction converts the kinetic energy into static (not-in-motion) energy. The more kinetic energy a vehicle has, the more heat is required to do the conversion.

    Disc brakes, as shown in the image to the right, have a good ability to dissipate the heat quickly (the RED areas), so that more heat can be used to bring the car to a complete stop.

    Gravity decreases your kinetic energy when you are driving uphill and increases it when you are driving downhill. Therefore, the force of gravity will make it:

  • easier to stop your car if you are going uphill
  • more difficult to stop your car if you are going downhill

  • Braking to a stop converts kinetic energy into heat energy in your brakes through friction. If you and your vehicle are involved in a collision, the kinetic energy is still converted into heat through friction, but not in your brakes (ouch!).

    Brakes heat up from friction when stopping a car.


    Lesson Summary


      

    Lesson 4 Quiz


    You will now answer 5 questions to test what you learned during this lesson. You must answer all questions correctly to receive completion credit for this lesson. You may answer the questions as many times as necessary to get them right.

    You should review the lesson material if you don't do well on the quiz.

    1. According to the formula for stopping distance, how many feet will it take you to stop, from 60 mph?


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    2. Centrifugal force:


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    3. Gravity:


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    4. The primary factor in decreasing the Kinetic Energy of an object is to:


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    5. The best way to maximize the traction of your tires is to:


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